1. Field of Invention
The present invention relates to micromechanical machines, and in particular to micromechanical mirrors used to direct light beams. This application is related to the subject matter disclosed in U.S. Pat. No. 5,835,256 to Huibers, and U.S. Pat. No. 6,046,840 to Huibers, the subject matter of each being incorporated herein by reference.
2. Related Art
FIG. 1 illustrates one architecture of an optical switch 2 (e.g. an optical cross-connect) using opposing micromechanical mirrors formed, for example, over a silicon substrate. Information carrying (modulated) light signals arrive through input optical fibers 100 that are each coupled to conventional input terminals 101. Each light signal is collimated into a light beam that is directed to one of several output optical fibers 102. Light beam directional steering is accomplished using the micromechanical mirrors in mirror arrays 104 and 106. Fine mirror tilt angle control is desirable to properly direct each light beam to one of several conventional output terminals 103, each coupled to one of the output fibers 102.
For example, a conventional information carrying light signal (e.g., modulated laser light) arrives though input fiber 100b. The signal exits the end of fiber 100b and is collimated by conventional optics (lens) to form light beam 110 that is incident on mirror 104b. Electrodes (not shown) deflect mirror 104b so as to direct beam 110 towards mirror array 106. The angle of deflection for mirror 104b is controlled by a switching algorithm that activates the electrodes such that light beam 110 is directed to the correct mirror in array 106. As depicted, mirror 104b directs beam 110 to mirror 106b, but alternatively may direct the beam to mirror 106a or 106c. The switching algorithm also actuates electrodes (not shown) that control the deflection angles of the mirrors in array 106, thereby directing light beams reflected from array 104 into the output fibers. As shown in FIG. 1, mirror 106a directs light into fiber 102a, mirror 106b directs light into fiber 102b, and mirror 106c directs light into fiber 102c. 
FIG. 2 illustrates a second architecture for another micromechanical optical switch 4. This second architecture uses a single micromirror array 120 and a fixed mirror 122 to produce a folded optical path. Input and output optical fibers are mixed in fiber array 124, and each fiber is coupled to conventional input or output terminals 125 as appropriate. Input light signals are collimated into a light beam and directed at a first mirror in array 120. The light beam is reflected from the first mirror in array 120 so as to reflect from fixed mirror 122 onto a second mirror in array 120. The second mirror is then angled to direct the light beam to the appropriate output fiber. For instance, FIG. 2 shows light beam 126 reflecting from mirrors 121a, 122, and 120b to reach output fiber 124b. FIG. 2 also shows mirror 120 alternatively tilted to a second angle so as to reflect beam 126 from mirrors 122 and 120c towards output fiber 124c. 
Architectures such as those illustrated in FIGS. 1 and 2 are preferable to cascaded binary cross-over switches for cross-connecting large numbers of optical fibers. A switch using one or two two-dimensional micromechanical mirror arrays can cross-connect, for example, 30xc3x9730 optical fiber arrays. In contrast, hundreds of cascaded binary cross-over switches would be required for such a cross-connect.
Micromechanical mirror configurations are known. FIG. 3 shows, for example, xe2x80x9creflective surfacexe2x80x9d 140 (shown in cutaway by dashed lines) that is xe2x80x9csuspended by four flexure hingesxe2x80x9d 142 and xe2x80x9cpostsxe2x80x9d 144 as disclosed in U.S. Pat. No. 5,808,780 [""780 patent]. Four xe2x80x9celectrodesxe2x80x9d 146a-d underlie reflective surface 140.
The ""780 patent states that the electrodes are xe2x80x9cactivated with a known analog voltage. The different levels of voltage available in the analog domain determine which of several deflected states the member assumes. Once a known analog voltage is applied, the segmented electrodes allow fine-tuning of the member""s positionxe2x80x9d in order to maintain the member parallel to it""s original position.
As the ""780 patent discloses, the embodiment illustrated therein has a mirror with only two stable positions, though the electrodes could allow a third stable position. The ""780 patent further states that the illustrated embodiment has only one input light path, though it could have two light paths passing light onto the reflective surface 32. The light could then be switched for one path or the other or both into one of four output paths for the two illustrated positions, or one of six output paths if there were a third position.
It is desirable to have an optical switch with at least one micromechanical mirror array, in which the mirror elements are capable of being deflected to a relatively large number of positions and angles, thereby permitting light beams from a large number of input fibers to be simultaneously directed to a large number of output fibers. Fine mirror tilt angle control is desirable, however, because the beam directed towards an optical fiber typically should be within a few tens of micrometers (xcexcm) of the output fiber""s end for sufficient light to enter the fiber. The control system that provides such fine control should be dynamic in order to compensate for mirror angle variations caused by temperature changes, for example. It is also desirable in some instances to use a digital control system to produce the electrostatic fields used to tilt the mirrors.
A light beam steering device includes a mirror plate that is mechanically coupled to an optically transmissive substrate by flexures that permit the mirror plate to tilt around a plurality of axes. The plate can be tilted in any direction (up to a tilt angle limit dictated by, e.g. the flexures and the tilt space). Therefore, an input light signal from an Nxc3x97N array can be directed to any output member on the same array or on a separate NxN output array. The optically transmissive substrate is spaced apart from a device substrate so that the mirror plate is between the optically transmissive and device substrates. Electrically conductive electrodes are formed on the device substrate opposite the mirror plate. The optically transmissive substrate can be fully or substantially transparent.
The mirror plate can be tilted in any direction, up to the tilt angle limit. The mirror is tilted to various angles by creating an electrostatic attractive force between the mirror plate and one or more selected electrodes. In addition, the mirror plate can be pulled away from the optically transmissive substrate by creating an electrostatic attractive force between the mirror plate and all electrodes. The electrodes can be formed in an array having various configurations. The electrodes in some electrode array embodiments receive analog (continuously variable) electric signals. The electrodes in other electrode array embodiments receive electric signals that are associated with one of two binary logic states.
The direction towards a target of the reflected portion of a light beam that is incident on the mirror plate is monitored and adjusted in various ways. In one embodiment the reflected portion of the beam is passed through a beam splitter. One split beam portion continues towards the target (e.g., output fiber) while another split beam portion is incident on a photodetector array. The position of the beam portion that is incident on the photodetector array correlates to the direction of the beam portion directed towards the target. An adjustment circuit uses information from the photodetector array to correct the direction of the beam portion that is traveling towards the target by adjusting the amount of charge on the electrodes under the mirror plate. In another embodiment, a second light source shines light, other than the information carrying light beam, onto the mirror plate. The reflected portion of light from the second light source is incident on a photodetector array. Since both the information carrying light beam and the second light source light are incident on the same mirror, the directions of the reflected portions of each beam are related. Thus the direction of the beam reflected towards the target is adjusted based on the incident position on the photodetector array of the reflected portion of light from the second source. In still another embodiment, photodetectors are positioned around the mirror plate to provide directional information associated with the beam that is incident on the mirror plate.
Therefore, in one embodiment of the invention, there is provided a light beam steering device comprising an optically transmissive substrate, a movable element held on the optically transmissive substrate by a plurality of flexures, with the flexures being coupled directly or indirectly to the optically transmissive substrate and the movable element. The flexures permit the movable element to tilt around a plurality of axes so as to deflect light incoming through the optically transmissive substrate back through the optically transmissive substrate. Also, a device substrate is provided spaced apart from the optically transmissive substrate such that the movable element is between the device substrate and the optically transmissive substrate.
Also provided is an optical switch comprising an optical fiber input terminal, an optical fiber output terminal, and a beam steering device comprising an optically transmissive substrate, a movable plate, and flexures extending from the movable plate and coupled directly or indirectly to the optically transmissive substrate. The flexures permit the movable plate to tilt around a plurality of axes so as to deflect light incoming through the optically transmissive substrate back through the optically transmissive substrate. A device substrate is provided spaced apart from the optically transmissive substrate such that the movable plate is between the device substrate and the Idoptically transmissive substrate.
An optical network is also provided which comprises at least one input fiber capable of carrying information at multiple wavelengths of light, one or more optical demultiplexers for separating multiple wavelengths of light from the at least one input fiber, an optical switch comprising an optical fiber input array comprising a plurality of optical fibers for providing a plurality of light wavelengths for switching, an optical fiber output array comprising a plurality of optical fibers for receiving a plurality of light wavelengths, and a beam steering device comprising an optically transmissive substrate, a plurality of movable elements, flexures extending from each movable element and coupled directly or indirectly to the optically transmissive substrate, and wherein the flexures permit each movable element to tilt around a plurality of axes so as to deflect light incoming from one of the plurality of optical fibers of the optical fiber input array and through the optically transmissive substrate back through the optically transmissive substrate to one of the plurality of optical fibers of the optical fiber output array. Also provided are one or more optical multiplexers for combining multiple wavelengths of light, and at least one output fiber capable of carrying information at multiple wavelengths of light.
Also provided is an optical beam scanner comprising a light source and a beam steering device comprising an optically transmissive substrate, a movable plate, and flexures extending from the movable element and coupled directly or indirectly to the optically transmissive substrate, and wherein the flexures permit the movable plate to tilt around a plurality of axes so as to deflect light incoming through the optically transmissive substrate back through the optically transmissive substrate. Also provided is a device substrate spaced apart from the optically transmissive substrate such that the movable plate is between the device substrate and the optically transmissive substrate, electrically conductive electrodes formed on the device substrate opposite the movable plate, wherein the light source is positioned to direct a light beam onto the movable plate of the beam steering device.